Numerous processes are within the purview of those skilled in the art for the preparation of toners. Emulsion aggregation (EA) is one such method. Emulsion aggregation toners may be used in forming print and/or electrophotographic images. Emulsion aggregation techniques may involve the formation of a polymer emulsion by heating a monomer and undertaking a batch or semi-continuous emulsion polymerization, as disclosed in, for example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in its entirety. Other examples of emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in U.S. Pat. Nos. 5,902,710; 5,910,387; 5,916,725; 5,919,595; 5,925,488, 5,977,210, 5,994,020, and U.S. Patent Application Publication No. 2008/0107989, the disclosures of each of which are hereby incorporated by reference in their entirety.
Polyester toners have been prepared utilizing amorphous and crystalline polyester resins as illustrated, for example, in U.S. Patent Application Publication No. 2008/0153027, the disclosure of which is hereby incorporated by reference in its entirety. The incorporation of these polyesters into the toner requires that they first be formulated into emulsions prepared by solvent containing batch processes, for example solvent flash emulsification and/or solvent-based phase inversion emulsification (PIE). In both cases, organic solvents, such as ketones or alcohols, have been used to dissolve the resins.
Polyester emulsions made via PIE may show polymer degradation over time. Polymers containing hydrolysable groups, for example hydrolysable carboxylic ester groups in polyester emulsions used for EA toners, have poor shelf life stability due to the water environment itself, biocides, pH conditions, ionic strength, and other additives such as surfactants and buffers. Hydrolyzed residual monomers and/or pendant acid groups on the polymer backbone resulting from polymer hydrolysis and/or polymerization of hydrolyzed monomer can become an enabler to further hydrolysis as the emulsion becomes more and more unstable.
A process of pH adjustment of polyester emulsions has been utilized to stabilize the emulsion and deter polymeric degradation over time as illustrated in U.S. Patent Application Publication No. 2010/0143839, the entire disclosure of which is hereby incorporated by reference in its entirety.
Methods which minimize the degradation and improve the shelf life of a resin emulsion prior to toner manufacture remain desirable.